Size of the mastoid air cell system obtained with two types of X-ray equipment.

The first systematically performed study concerning the size variation of the mastoid air cell system was measured on the X-ray film in a lateral projection, as exposed on the skull table. A new type of equipment (Orbix) with an isocentric motion of the roentgen tube and the film cassette and a different magnification, is gradually replacing the skull table. Temporal bone specimens were examined in a lateral projection using both equipments. The area of the mastoid air cell system was measured with a planimeter. A significant correlation was found between the areas obtained with the two techniques.